You are reading Part 5 of 9 in this series.What are Quick Facts?
Evidence continues to mount that human-induced climate change is causing hurricanes to grow stronger and more destructive. Hurricanes are producing heavier rain, their storm surges are riding atop higher sea levels, and in many cases they are lingering longer over land, causing increased flooding and infrastructure destruction.
Facts for Any Story
The five costliest U.S. Earth-system disasters (including earthquakes, volcanic eruptions, fires, and all kinds of extreme weather, adjusted for inflation) have all been hurricanes, and all five have occurred within the past 15 years: Harvey (2017), Katrina (2005), Sandy (2012), Irma (2017), and Maria (2017).1NOAA Office for Coastal Management: Hurricane Costs View Source2Statista, 2020, Most expensive natural disasters in the United States as of April 2020 View Source
Hurricanes get their energy from ocean heat; the warmer the water is, the stronger a hurricane can get. More than 90% of the excess heat trapped in the climate system due to human-caused global warming has gone into the oceans, providing the added energy driving recent hurricanes’ extreme wind intensities and the increased evaporation that has resulted in associated torrential rainfall.3IPCC, 2014, Synthesis Report, Summary for Policymakers, p. 4. View Source
Globally, the last few decades have seen a growing proportion of strong hurricanes and a corresponding shrinking proportion of weak ones. Specifically, from 1975 to 2010, the proportion of Category 4 or 5 hurricanes (the highest wind speeds) increased by 25-30 percent for every 1 degree Celsius increase in global temperature due to human causes, resulting in a near doubling of the proportion of those most intense hurricanes.4Holland, G. et al., (2014), Climate Dynamics, 42, 617. View Source
Both heavy rain and storm surge—water pushed ashore by heavy winds—contribute to flooding, which causes the vast majority of hurricane-related deaths and financial losses. The amount of rain falling in recent hurricanes has increased due to climate change, including in Harvey (by 20 to 38 percent),5Risser, M. D., et al., (2017), Attributable human-induced changes in the likelihood and magnitude of the observed extreme precipitation during hurricane Harvey, Geophys. Res. Lett., 44, 12457–12464, and Wang, S. Y. et al., (2018) View Source6Wang et al., Quantitative attribution of climate effects on Hurricane Harvey’s extreme rainfall in Texas, Env. Res. Lett., 13, 054014. View Source Katrina, Irma, and Maria. 7Patricola, C. and Wehner, M., (2018), Anthropogenic influences on major tropical cyclone events, Nature, 563, 339–346. View Source Hurricanes are also producing higher storm surges due to sea level rise.8Rahmstorf, S., (2017), Rising hazard of storm-surge flooding, PNAS, 114 (45), 11806-11808 View Source
Climate-change-related perturbations in atmospheric winds like the jet stream appear to be contributing to a trend in which hurricanes are moving more slowly over the United States9Rahmstorf, S., (2017), Rising hazard of storm-surge flooding, PNAS, 114 (45), 11806-11808 View Source (slowing by 17% over the past century),10Kossin, J. P., (2019), Matters Arising, Reply to Moon et al. and Lanzante, J.R.. Nature, 570, E16-E22. View Source and are increasingly likely to “stall” near the coast, potentially leading to catastrophic local rainfall and flooding. 11Hall, T. M. and Kossin, J. P., (2019), Hurricane stalling along the North American coast and implications for rainfall, Climate and Atmospheric Science. View Source12Zhang, Gan, (2020), Tropical cyclone motion in a changing climate, Science Advances, 6:17. View Source
There has been a significant increase in how quickly hurricanes intensify in the Atlantic basin in recent decades, an expected symptom of global warming.13Bhatia et al., (2019), Recent increases in tropical cyclone intensification rates, Nature Communications, 10, 635. View Source Hurricanes that intensify rapidly are difficult to forecast accurately and prepare for, especially when this occurs close to the coast, and cause a disproportionate amount of human and financial losses.14Emanuel, K., (2017), Will global warming make hurricane forecasting more difficult?, Bulletin of the American Meteorological Society, 98, 495-501. View Source
Globally, hurricanes are reaching their maximum intensities further from the tropics, shifting toward temperate, heavily populated coastal regions that have not historically experienced them. Northern Hemisphere hurricane peak intensities have shifted northward by 100 miles in the past 30 years.15Kossin, J. P., et al., (2014), The poleward migration of the location of tropical cyclone maximum intensity. Nature, 509, 349-352. View Source
Pitfalls to Avoid
Avoid asking whether climate change “caused” a particular hurricane to slow, intensify rapidly, etc., as there are always many contributors to any weather event. Instead, ask whether climate change contributed to the intensity of a hurricane or the likelihood of its especially damaging behavior (such as stalling over a coastline)—questions that scientists can increasingly answer with confidence given recent advances in attribution science.
Dr. James Kossin
National Oceanic and Atmospheric Administration, National Centers for Environmental Information